# Vignetting correction on a fish-eye HDR image

Hi,

I am trying to fix vignetting on fish-eye HDR images. I found this post in
HDRI archive:

I am still confused on how to use pcomb to fix vignetting.
Can anyone help me wright the pcomb script using the following polynomial
function:

y = -1.28E -12 * x 4 + 3.43E - 09 * x3 - 3.38E - 06 * x2 +1.45E - 03 * x +
7.70E - 01

Thank you,

Leyla Sanati
Ph.D Candidate
UW-Milwaukee

Hi Leyla,

Assuming this function describes the fall-off as a function of eccentricity (distance from image center), and the edge of the image is the edge of your circle corresponding to x==1 in your formula, you could try:

pcomb -e 'sq(x):x*x;r=sqrt(sq(2/xres*x-1)+sq(2/yres*y-1))' \
-e 'sf=-1.28E-12*r^4 + 3.43E-09*r^3 - 3.38E-06*r^2 +1.45E-03*r + 7.70E-01' \
-e 'ro=sf*ri(1);go=sf*gi(1);bo=sf*bi(1)' input.hdr > corrected.hdr

I think I must be misunderstanding your function, though, because it plots as a (nearly) straight line that increases from 0.7700 at x==0 to 0.7714 at x==1. This doesn't seem a likely vignetting correction, as it should go down rather than up, and by a more significant amount.

Best,
-Greg

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From: Leyla Sanati <[email protected]>
Date: September 21, 2012 8:36:07 AM PDT

Hi,

I am trying to fix vignetting on fish-eye HDR images. I found this post in HDRI archive: